Vehicles having a hybrid drive structure have an internal combustion engine and typically an electric motor as a second drive unit. The drive torque may thus be applied by both drive assemblies during the driving operation of the hybrid vehicle.
In a so-called parallel hybrid, the electric motor is situated on the shaft of the internal combustion engine, the electric motor being connected to the internal combustion engine via a clutch. If the hybrid vehicle is solely driven by the electric motor, the power of the hybrid vehicle is limited by a maximum drive torque of the electric motor. If this maximum drive torque is no longer sufficient to meet the driver intention for further acceleration of the hybrid vehicle, the clutch is engaged, the electric motor dragging the internal combustion engine and thus starting it. From this point in time, both the electric motor and the internal combustion engine contribute to driving the hybrid vehicle.
During the internal combustion engine start phase, the electric motor must apply the drag torque for the internal combustion engine in addition to the vehicle drive torque. It may occur that the electric motor can no longer provide sufficient torque for the simultaneous drive of the hybrid vehicle and the drag torque, since the available drive torque decreases in the event of a rising speed of the electric motor, for example. In this case, the vehicle acceleration collapses with an uncomfortable jerk which is perceptible by the driver.